Re: [PATCH v7 5/7] arm64: ipi_nmi: Add support for NMI backtrace

[Masayoshi Mizuma]

On Mon, Nov 02, 2020 at 05:14:45PM +0530, Sumit Garg wrote:
> Enable NMI backtrace support on arm64 using IPI turned as an NMI
> leveraging pseudo NMIs support. It is now possible for users to get a
> backtrace of a CPU stuck in hard-lockup using magic SYSRQ.
> 
> Signed-off-by: Sumit Garg <sumit.garg@xxxxxxxxxx>
> ---
>  arch/arm64/include/asm/irq.h |  6 ++++++
>  arch/arm64/kernel/ipi_nmi.c  | 18 ++++++++++++++++--
>  2 files changed, 22 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/irq.h b/arch/arm64/include/asm/irq.h
> index b2b0c64..ef018a8 100644
> --- a/arch/arm64/include/asm/irq.h
> +++ b/arch/arm64/include/asm/irq.h
> @@ -6,6 +6,12 @@
>  
>  #include <asm-generic/irq.h>
>  
> +#ifdef CONFIG_SMP
> +extern bool arch_trigger_cpumask_backtrace(const cpumask_t *mask,
> +					   bool exclude_self);
> +#define arch_trigger_cpumask_backtrace arch_trigger_cpumask_backtrace
> +#endif
> +
>  struct pt_regs;
>  
>  static inline int nr_legacy_irqs(void)
> diff --git a/arch/arm64/kernel/ipi_nmi.c b/arch/arm64/kernel/ipi_nmi.c
> index a945dcf..597dcf7 100644
> --- a/arch/arm64/kernel/ipi_nmi.c
> +++ b/arch/arm64/kernel/ipi_nmi.c
> @@ -8,6 +8,7 @@
>  
>  #include <linux/interrupt.h>
>  #include <linux/irq.h>
> +#include <linux/nmi.h>
>  #include <linux/smp.h>
>  
>  #include <asm/nmi.h>
> @@ -31,11 +32,24 @@ void arm64_send_nmi(cpumask_t *mask)
>  	__ipi_send_mask(ipi_nmi_desc, mask);
>  }
>  
> +bool arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
> +{
> +	if (!ipi_nmi_desc)
> +		return false;
> +
> +	nmi_trigger_cpumask_backtrace(mask, exclude_self, arm64_send_nmi);
> +
> +	return true;
> +}
> +
>  static irqreturn_t ipi_nmi_handler(int irq, void *data)
>  {
> -	/* nop, NMI handlers for special features can be added here. */
> +	irqreturn_t ret = IRQ_NONE;
> +
> +	if (nmi_cpu_backtrace(get_irq_regs()))
> +		ret = IRQ_HANDLED;
>  
> -	return IRQ_NONE;
> +	return ret;
>  }
>  
>  void dynamic_ipi_setup(int cpu)
> -- 

It works well with sysrq l trigger.
Please feel free to add:

	Tested-by: Masayoshi Mizuma <m.mizuma@xxxxxxxxxxxxxx>

Thanks!
Masa